Background: We recently discovered that individuals with complete spinal cord injury (SCI) have a higher grip force control ability in their intact upper limbs than able-bodied subjects. However, the neural basis for this phenomenon is unknown.
Objective: This study aimed to investigate the neural basis of the higher grip force control in the brains of individuals with SCI using multimodal magnetic resonance imaging (MRI).
Methods: Eight SCI subjects and 10 able-bodied subjects performed hand grip force control tasks at 10%, 20%, and 30% of their maximal voluntary contraction during functional MRI (fMRI). Resting-state fMRI and T1-weighted structural images were obtained to investigate changes in brain networks and structures after SCI.
Results: SCI subjects showed higher grip force steadiness than able-bodied subjects (P < .05, corrected), smaller activation in the primary motor cortex (P < .05, corrected), and deactivation of the visual cortex (P < .001, uncorrected). Furthermore, SCI subjects had stronger functional connectivity between the superior parietal lobule and the left primary motor cortex (P < .001, uncorrected), as well as larger gray matter volume in the bilateral superior parietal lobule (P < .001, uncorrected).
Conclusions: The structural and functional reorganization observed in the superior parietal lobule of SCI subjects may represent the neural basis underlying the observed higher grip force control, and is likely responsible for the smaller activation in the primary motor cortex observed in these individuals. These findings could have applications in the fields of neurorehabilitation for improvement of intact limb functions after SCI.
Keywords: brain reorganization; force control; magnetic resonance imaging; primary motor cortex; spinal cord injury; superior parietal lobule.